Fifteen Cards

Stage: 2 Challenge Level:

I have fifteen cards numbered $1 - 15$.

I put down seven of them on the table in a row.

The numbers on the first two cards add to $15$.
The numbers on the second and third cards add to $20$.
The numbers on the third and fourth cards add to $23$.
The numbers on the fourth and fifth cards add to $16$.
The numbers on the fifth and sixth cards add to $18$.
The numbers on the sixth and seventh cards add to $21$.

The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the
NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to
embed rich mathematical tasks into everyday classroom practice. More information on many of our other activities
can be found here.